1. Field of Invention
This invention relates to antennas suitable for digital signals to increase the gain for receiving and/or transmitting signals in the Ultra High Frequency (UHF) and/or Very High Frequency (VHF) ranges.
2. Description of the Related Art
Marginal Performance: Digital Television (DTV) including High Definition Television (HDTV) is displacing analog TV because of its much higher image resolution. However, DTV requires minimum signal level to be useable. DTV signals below this threshold level typically result in no picture at all. E.g., while the US Federal Communications Commission (US FCC) requires a minimum 15.2 dBa Signal/Noise ratio, signals often cut out below about 17 dBa Signal to Noise (S/N) ratio compared to a strong signal having a S/N ratio of about 33 dBa. Multipath signals can cause serious reception problems, especially in urban areas. Signals with borderline Signal/Noise ratios result in pixilation and other unacceptable distortions. Relevant art UHF antennas are typically configured for at higher frequencies than the USA's digital TV channel allocations. Antennas designed UHF half wave dipole resonance have low VHF performance. The US FCC expects that many consumers will need to obtain new antennas for free to air DTV reception.
Corrosion: Typical antenna installations allow moisture to enter coax connectors and coax lines. This causes outside and even inside connector corrosion resulting in major signal attenuation over time. Many antennas use steel rivets or screws to hold aluminum elements, or to connect copper cables to steel connectors. Galvanic action corrodes contacts, increasing electrical impedance and degrading signal reception and/or transmission over time.
Wear: VHF and UHF antennas are commonly folded for shipment. Wind flexing of riveted or screwed elements causes joint movement and wear, loosens connections, and increases signal loss with time. Flimsy plastic or light metal element mounts frequently break, bend, or work loose in storms. Miss-alignment and/or loose or lost connections seriously degrade antenna gain.
Impedance mismatch: Most VHF prior relevant art utilizes 300 ohm antenna feed points. These antennas require impedance converters (“baluns”) from 300 ohm antenna feed points to 75 ohm (or 52 ohm) cable with corresponding extra connection points. With VHF/UHF antennas, such baluns typically causes 1.5 dB to 6 dB insertion losses with UHF signals, attenuating a major portion of the typical 4 dB to 8 dB UHF antenna gain.
Cable loss: Even using quality RG-6 75 Ohm coax cable, high UHF signals are often attenuated within the connecting cable by 50% to 75% or more of the signal gain obtained by high gain antenna. E.g., the FCC (2005) expects signal attenuation of about 4 dB for a 15 m (50 ft) downlink for 470-800 MHz (Channels 14-69) signal in RG-6 coax cable compared to an 8 dB gain using a good Yagi UHF antenna.
Increased Transmission: Digital TV transmission is often increased to 1,000 kW or more to accommodate higher losses and minimum S/N reception requirements. Relevant art antenna amplifiers (or “preamps”) configured for 50 kW transmission often saturate and distort (“splatter”) when receiving such stronger DTV TV transmissions. This can cause digital signal dropout, especially near high power TV transmitters.
Generic performance: Increasing propagation distances and signal degrading environments are commonly categorized as “Urban, “Suburban”, “Far Suburban”, “Mid Fringe” and “Deep Fringe” reception regions. Generic broadband antenna systems are typically unnecessarily expensive if used near to transmitters in Urban and even Suburban areas. Yet they may be marginal in Mid Fringe areas and are often unusable in Deep Fringe areas.
Complex: Numerous antenna systems are complex and difficult to install with confusing instructions. E.g., one prior art high gain VHF/UHF antenna shown in FIG. 23 (see U.S. Pat. No. 3,531,805). As further depicted in that prior art, VHF antenna supports often use highly complex VHF elements with numerous mounting components and phasing lines. These have numerous contacts and mounts that are prone to corrosion, wear and failure. Long elements are often folded for shipping and users frequently do not unfold elements. FIG. 24 shows the corresponding short 168 mm (6.63″) prior art “Peterson” folded VHF/UHF driven dipole element. Such relevant art UHF designs are no longer optimized for UHF DTV signals.
Low VHF/UHF reception: The US Federal Communications Commission (Dec. 2005 Report 05-199) plans on antennas with 6 dB gain for the VHF High Band with a Front/Back ratio of 12 dB for distant DTV signals in “Fringe” areas. This FCC (2005) report plans on 10 dB gain for the UHF band with a Front/Back ratio of 14 dB. The conventional art uses large VHF antennas to achieve such VHF performance, especially for fringe regions. Most UHF antennas marketed for the Digital TV exhibit very low VHF gain. UHF enhancing screens of relevant art high gain UHF antennas show low VHF reception. Similarly a good UHF Yagi antenna while providing modest UHF gain, provides very little VHF reception. Many antennas advertised for VHF/UHF reception are described by third party evaluators as exhibiting marginal performance in the UHF range and very poor performance in the VHF range.
Low Signal/Noise Ratios: Analog TV or NTSC transmission, results in progressively degraded and increasingly fuzzier reception with increasing distance, intervening vegetation, and/or multipath signal transmission. While degraded, analog audio can often still be understood. However, amplifying signals with low antenna gain and/or long lossy lines degrades signal/noise ratios. This can cause instability or total dropout with both video and audio reception of DTV signals.
Physical Unattractiveness: Most high performance broadband VHF/UHF antennas have large obtrusive Log periodic structures or numerous bowtie elements with large screens. Small unobtrusive antennas give poor performance, especially in the VHF High Band range.
Wind loading: Relevant art antennas typically use box channel or cylindrical VHF elements resulting in substantial wind loading and wear.